Hepatitis C virus infections affect approximately 2% of the population and often progress to cirrhosis and liver cancer. Some of the characteristics associated with a failed adaptive immune response in chronic infection have been identified, yet the events that precede and determine the failed immune response are less clear and may involve the innate immune response. Research on HCV has been impeded by the lack of a small animal model. In this proposal, we will use GBV-B infected marmosets in an innovative approach to evaluate knockdown of a series of target genes involved in the innate immune response. GBV-B is the virus most closely related to HCV and it induces hepatitis in marmosets and tamarins. The central hypothesis of this project is that the innate immune response is essential for limiting viral spread in the liver and for orchestrating the adaptive immune response for the successful clearance of infected cells. Knockdown of critical components of the innate response may lead to extended duration of viremia and potentially persistent infections. In collaboration with Santaris Pharma, we recently demonstrated the ability of systemically administered LNA (locked nucleic acid) oligos to knockdown genes in a primate model; the knockdown of microRNA-122 in chimpanzees effectively reduced HCV viral load. Chimpanzees are too large and expensive for use in most research projects. Marmosets are ideal for this project due to the small size and the fact that they normally clear GBV-B infection, one of the few differences from HCV. Persistent infections beyond one year have been observed, thus the capacity for persistence clearly exists. In aim 1, we will target miR122 using the same LNA antisense oligo as the Santaris drug, SPC3649. This will serve as a positive control to evaluate the kinetics and magnitude of LNA knockdown in the marmoset. In aim 2, we will knockdown IL28B and its receptor IL28RA. In man polymorphisms in IL28B are highly predictive of persistent infection with HCV, yet we have little understanding of how IL28B influences HCV infection. In aim 3, we will knockdown TLR7, the primary receptor on plasmacytoid dendritic cells sensing viral RNA and triggering IFN production. We will also knockdown BST2, the receptor that provides negative feedback to pDCs and controls IFN production. In aim 4, we will knockdown the sensors of viral RNA in the liver leading to IFN production including RIG-I, TLR3 and IRF3. Although, HCV protease subverts both these pathways, the role this plays in vivo in the spread of virus and induction of ISGs in the liver is poorly understood. Collectively, these studies will help define the role of various components of the innate immune response in viral clearance and potentially new approaches to therapies for chronic infections. In addition, persistent GBV-B infections would represent a new primate model for HCV disease progression. Furthermore, development of a primate model of targeted gene knockdown would be of great value in a number of research areas.